The invention concerns a method for the detection of influenza A/B viruses, a corresponding test kit and the use of saliva as a sample material for the detection of influenza A/B viruses.
Influenza is a frequently underestimated infectious disease which can result in high morbidity and mortality rates especially in elderly persons and in high-risk patients. Influenza A and/or influenza B viruses (also abbreviated influenza A/B viruses in the following) are responsible for genuine virus influenza which is contracted by several 100 million persons worldwide each year. The influenza A and B viruses primarily infect the nasopharyngeal and oropharyngeal cavities and initially cause general respiratory symptoms in the affected persons.
It is not possible even for experienced medical professionals to very reliably diagnose influenza solely on the basis of the patient""s clinical symptoms since other viruses which infect the nasal or pharyngeal cavity such as adenoviruses, parainfluenza viruses or respiratory syncitial viruses (RS viruses) cause similar symptoms.
Due to the high medical importance of influenza infections (flu), almost every country in the world now has a nationally organized influenza monitoring system. For this scheme general practioners remove swabs from the nose and/or throat and send them to the respective national reference centre. The influenza A/B viruses are then usually detected by eluting the swabs and subsequently culturing the patient specimens on mammalian cells such as MDCK cells (Madine-Darby Canine Kidney cells).
The culture in these special laboratories can take up to 14 days and is thus not of immediate relevance for the diagnosis of the individual patients. Rather the goal of the national reference centres is to type and subtype the cultured viruses and to report the results to the World Health Organisation (WHO). The job of the vaccine manufacturer is then to adapt next year""s influenza vaccines to the latest circulating viral strains on the basis of the annual WHO recommendation.
The reason for the high degree of genetic and hence immunological variability especially of the influenza A viruses is due to the fact that a genetic shift (reassortment of the viral genes) can also occur in rare cases in addition to the usual genetic drift (point mutation). This is due to the fact that, in contrast to other viruses, the genome of the influenza viruses is segmented and that influenza A is a pathogen in humans as well as in animals.
The immunodominant antigens present on the surface of the virus are haemagglutin (H) and neuraminidase (N). At present 15 subtypes of haemagglutin (H1-H15) and 9 subtypes of neuraminidase (N1-N9) are known for influenza A.
If for example a host (e.g. a pig) is coinfected with an influenza virus of the A type which is pathogenic for man and with an influenza A bird virus this can result in a reassortment of the viral genome to form a new influenza A virus subtype which then completely evades the human immune system when it is transferred back to humans. The most recent example of this was the occurrence of the so-called avian virus influenza in May 1997 in Hong Kong (type A/H5N1/Hong Kong/156/97) in which 6 of the 18 affected patients died despite an early detection and intensive medical care.
However, in order to cause a larger epidemic or even a worldwide pandemic, a new influenza virus subtype must be transmitted directly from human to human as was the case in 1918/1919 for the first occurrence of the subtype H1N1 (Spanish flu, worldwide ca. 50 million deaths), 1957 (H2N2, Asian flu, ca. 1 million victims) and 1968 (H3N2 Hong Kong flu, ca. 1 million victims).
A new generation of influenza agents has recently become available, the so-called neuraminidase inhibitors which for the first time allow a causal treatment of influenza and are thus regarded among experts as a true breakthrough in the treatment of influenza. Clinical studies carried out for the registration of this new class of substance showed that successful treatment primarily depends on an early start to treatment after the first clinical symptoms occur. Hence in view of this new therapeutic option, the necessity to begin the treatment at an early stage and the relatively unspecific clinical symptoms, a rapid individual diagnosis would be helpful as a basis for treatment decisions.
As a result several diagnostic manufacturers have recently developed rapid immunological influenza tests based on antigen detection and these rapid tests are nasal and/or throat swabs or liquid obtained by nasal irrigation as the sample material. Examples of such rapid influenza tests are the Influenza A/B Rapid Test from Roche Diagnostics GmbH, Quick Vue(copyright) from Quidel and AB FLU OLA(copyright) from Biostar.
A particular problem in collecting samples is to remove sample material from the affected region of the nasal and pharyngeal cavity which contains sufficient amounts of influenza A and/or influenza B viruses (abbreviated to influenza A/B viruses in the following). Hence the quality of sampling has a direct influence on the positivity rate of the rapid tests which usually have a clinical sensitivity of about 70% i.e. the immunological rapid test is also positive in 70% of all samples that are assessed to be influenza positive by the reference method (cell culture). Hence the diagnostic manufacturers point out in the package inserts for their influenza rapid tests that the specimens should only be collected by specially trained medical personnel in order to ensure that the specimen material obtained does in fact contain adequate amounts of influenza A/B viruses.
The situation is further complicated by the fact that the regions in the pharyngeal cavity that have to be swabbed (posterior pharyngeal wall, pharynx, tonsils) can indeed differ depending on the viral infection that is present. This for example means that a swab has to be taken of other regions of the throat in order to detect a streptococcal infection than for example to detect influenza A/B viruses.
Taking a nose/throat swab is unpleasant for patients and a particular problem in the case of (small) children. On the other hand children are the main carriers of virus influenza at least in the early phase of an influenza epidemic due to their social contacts (kindergarten, school) and the fact that their immune system is often not yet fully developed.
Since nose and throat swabs are not a homogeneous sample material, the positivity rate of an influenza test is, in addition to the quality of the swab, also determined by the correct elution i.e. the transfer of the swab material to a liquid phase which then serves as the actual sample material in the subsequent test.
Especially the new therapeutic option (neuraminidase inhibitors) will in future result in an increasing need for flu virus tests (influenza A/B viruses) for general practitioners or the patients which is not compatible with the previously used sample material (swab, nasal irrigation) that requires that specimens be taken by trained (medical) personnel.
The object of the present invention is to eliminate the disadvantages of the prior art. In particular the object of the invention is to provide a method for detecting an influenza A and/or influenza B virus infection which can be carried out by untrained personnel or ideally by the patients themselves. Above all it is an object of the invention to find a sample material from which influenza A and/or influenza B viruses can be reliably detected which is preferably homogeneous and can be collected by untrained personnel or ideally by the patient themselves in a simple and uncomplicated manner.
The invention concerns a method for the detection of an infection with the influenza A and/or influenza B virus comprising the steps
i) obtaining a saliva sample from the individual to be examined
ii) preparing the saliva sample for the detection or a detection reaction and
iii) detecting the influenza A and/or influenza B virus in the saliva sample.
The invention additionally concerns a test kit for detecting an infection with the influenza A and/or influenza B virus containing
i) a device for collecting a saliva sample and
ii) reagents and auxiliary agents for the detection of influenza A and/or influenza B viruses.
Finally the invention concerns the use of saliva as a sample material to detect an infection with the influenza A and/or influenza B virus.